When constructing detectors such as this, great care must be paid to cleanliness, dimensional accuracy and quality control, because small quantities of foreign matter can drastically reduce the reliability of the detector apparatus. Thus, where cylindrical or spherical seismic elements are mounted on wire supports, there are only point contacts or, at most, line contacts between the electrically conductive members. This means that a small amount of non-conducting foreign material can render the operation of the detecting apparatus unacceptably inaccurate in that the open circuit condition will be indicated far too frequently as a result of the contacting surfaces being separated by insulating foreign matter.
One technique which has been utilised to overcome this deficiency is the use of two or more seismic elements which are mounted on separate or common supports so as to provide parallel electrical paths which are each connectable to the vibration detecting circuits. However, although this technique results in a marked improvement in reliability of the vibration responsive detectors constructed in this way, these detectors are relatively expensive to manufacture, for the improvement obtained, and it is necessary to construct these detectors under the same stringent conditions necessary when constructing vibration responsive detectors having only one seismic element each.